Pipe sections may be joined by a number of means including welding, gluing or the use of threaded couplings. Traditionally, threaded couplings involve two, three or four components. In one such device, two tube lengths, each one having a shoulder at one end may be joined by two mating elements, which slide over the tube length, one mating element having external threads, the other element having internal threads. In all, four elements must be brought together to carry out the mating process. Similarly, in a three element mating process, one tube length may have external threads to be mated to an internally threaded element which slides over a non-externally threaded tube length. Finally, both tube lengths may themselves have threaded sections which mate directly.
These traditional threaded couplings used to join two lengths of tubing suffer from a number of shortcomings. These include, the total number of elements needed to complete the mating process, the likelihood of improper alignment of the elements leading to screw-thread damage, and the inconvenience of multi-turn rotation of at least one of the elements in order to complete the mating process.
In an effort to reduce the number of such shortcomings or to reduce the severity therefrom, there have been developed threaded pipe couplings in which the threaded sections of the mating components are segmented, interposed by an equal number of nonthreaded or plain segments. The primary advantage of such schemes has been to reduce the rotational motion of the mating elements to less than one full turn.
U.S. Pat. Nos. 112,958 and 3,540,762 (the disclosures of which are incorporated herein by reference), are examples of three element couplings with segmented threads. The disadvantage of these designs is in the number of components required which reduces the ease and speed of connecting and disconnecting the assembly.
U.S. Pat. Nos. 222,713 and 1,629,058 (the disclosures of which are incorporated herein by reference), are examples of two element segmented thread couplings. One disadvantage of each of these designs is the small size of such threads. By reducing the amount of thread surface, there is a corresponding reduction in the strength of the coupling.